Protein N-glycosylation is an essential process in yeast, C. elegans, mouse and man. Animal species express numerous glycoproteins that participate in a constellation of discrete biological processes. The severe multisystemic syndromes that occur in children with viable congenital defects dramatically demonstrate this. N-glycans also regulate tumor growth and metastatic potential. To understand the roles of N-glycosylation in normal development and the pathology caused by defects, a means to determine which of the myriad possible glycoproteins, (i) functionally depend on N-glycosylation, and (ii) participate in fundamental effector processes is required. The intrinsic pleiotropy and cellular non-autonomy of N-glycosylation confounds this; mutational or pharmacological approaches that perturb N-glycan synthesis alter all glycoproteins, molecules that characteristically function in intercellular processes. This proposal exploits the power of Caenorhabditis elegans genetics to overcome these difficulties. Dauer larva formation in C. elegans is a paradigm for the integration of environmental and neuroendocrine signals to resolve developmental alternatives. A genetic network of over 100 genes involving several pathways conserved in all metazoans, such as the PI3-kinase and TGFbeta pathways, controls dauer switching in C. elegans. N-glycan biosynthesis in nematodes approximates that of humans and we have observed that N-glycosylation modulates dauer development. By screening for C. elegans mutants that form dauer larvae constitutively only when N-glycosylation is compromised, we will isolate alleles of genes whose products depend on Nglycans for wild type activity, effectively the genes downstream of the glycosylation pathway that elaborate the dauer phenotype. These synthetic dauer constitutive mutations will be mapped, cloned, and positioned with respect to the known genetic network using established C. elegans methods. The definition of specific effector pathways modulated by N-glycosylation dependent proteins will reveal how glycosylation contributes to this model of developmental decision-making. Since all metazoans conserve the genetic pathways that determine dauer formation, it is plausible that homologous gene-products and processes are affected in mammals thereby closing the hermeneutic circle.